gcd_2_2[2] := 1;
gcd_2_2[4] := 1;
gcd_2_2[6] := 1;
gcd_2_2[8] := 1;
gcd_2_2[10] := 1;
gcd_2_2[12] := 1;
gcd_2_2[14] := 1;
gcd_2_2[16] := 1;
gcd_2_2[18] := 1;
gcd_2_2[20] := 1;